This invention relates to a method for the determination of thermal properties such as thermal conductivity, thermal diffusivity and thermal capacity by arbitrary heat input under an arbitrary boundary condition and under arbitrary initial conditions, with the initial temperature distribution kept in a certain limited condition.
For virtually all industries, especially those currently being urged to adopt effective measures concerning the consumption of energy, and for various academic branches in the natural sciences as well, the numerical values of thermal properties have great significance. The methods heretofore practiced in the determination of thermal properties are broadly divided into a steady method and a non steady method which is based on the analytical solution of the basic heat conduction equation. The steady method (reviewed by Tye, R. P., Thermal Conductivity, Vol. 1-2 (1969), Academic Press) has found widespread acceptance. Nevertheless, this method entails a practical difficulty in having the temperature maintained in a necessary steady state. The measurement by this method takes much time and calls for advanced skill.
The non steady method which is based on analytical solution (reviewed Kobayashi, K., J. of JSME, 77-668 (1974), 754) has recently achieved a notable growth in acceptance. To materialize experimentally the ideal boundary condition used for obtaining the analytical solution, meticulous care is needed and the apparatus used therefor is generally complicated and expensive. The characteristic common to the various methods described above resides in the difficulty experienced in establishing the boundary condition of the given sample with an ideal steady condition, stepped value and so on. This fact has made the determination of thermal properties extremely difficult.
To meet today's need for accurate data on thermal properties, there must be provided a method which is capable of reducing the necessity for establishing the boundary condition. As one such method, there may be cited the method which is based on the numerical calculation. With this method, however, the arbitrariness is limited and the calculation is fairly complicated. At this stage, there is no indication that this method will find popular acceptance.
The only proposed method (Kavianipour, A. and Beck, J. V., Int. J. Heat Mass Transfer, 20, (1977), 259) which involves a principle similar to the principle of the present invention is intended for sole application to semi-infinite solid articles as the subject of determination. For the purpose of simultaneous determination, this method inevitably involves bringing the given sample into abrupt contact with an article of an elevated temperature and calculating the change in the heat flow rate on the basis of the average temperature change occurring in that article. Thus, the boundary condition involved therein can hardly be called perfectly arbitrary. Moreover, the range of determination allowable by this method is limited and the method itself suffers from the disadvantage that the determination admits of a heavy error due to heat loss and other factors.
The development of a method which, unlike the conventional method, permits thermal properties to be determined by a procedure comparable with any of the conventionally practiced procedures in a system wherein the boundary condition is perfectly arbitrary and the heating condition is also entirely arbitrary can be expected to make a notable improvement in terms of equipment, process and accuracy.